Argo CD Image Updater CVE-2026-121621

Exploitation requires the attacker to be able to set the proxy URL on an SSH Git repository consumed by Argo CD Image Updater, and the vulnerable code path is the SSH credential handling that passes that proxy value unsanitized into a shell-interpreted SSH command (ProxyCommand/GIT_SSH_COMMAND, via connect-proxy). The deployment must therefore use SSH Git credentials with a proxy configured. Limiting factors: the attacker needs existing privilege to create or modify the repository/proxy configuration (consistent with CVSS PR:L), so this is not anonymous exploitation; the fixed releases reject non-conforming proxy URLs (allow-listed schemes socks5/socks5h for SSH, safe hostname characters only, valid port) which closes the path. Per the vendor fix, upgrading to a patched release is the remediation.

This is a credible, action-worthy issue but not an emergency. The input CVSS vector (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H, base 8.8) indicates a network-reachable, low-complexity flaw requiring some existing privilege (PR:L) and no user interaction, with full compromise of confidentiality, integrity, and availability within the Image Updater process scope. The exploitation mechanism is well-understood from the source evidence: the fix PR (argocd-image-updater #1905) adds strict proxy-URL validation (scheme allow-listing, hostname character regex, IPv6/port checks) precisely because a proxy value was being interpolated unsanitized into a shell-interpreted SSH ProxyCommand/GIT_SSH_COMMAND - this directly corroborates the CWE-78 command-injection description rather than relying on paraphrase. The vuln.today decision label is 'this_week', consistent with a serious-but-not-active-exploitation posture. No EPSS score, no CISA KEV listing, and no public exploit were provided in the input, so there is no signal of widespread or active exploitation; the only linked code is the vendor fix, not a working exploit. The main qualifier on real-world risk is the PR:L requirement: an attacker must already be able to set the proxy field on an SSH Git repository definition, which limits this to actors with some level of repository/configuration access rather than fully anonymous internet attackers. EPSS and KEV data are missing, so exploitation probability cannot be quantified from the provided signals - treat urgency as governed by the 'this_week' decision label.

An attacker who can define or edit an SSH Git repository used by Argo CD Image Updater sets the repository's proxy URL to a value containing shell metacharacters. When Image Updater builds the shell-interpreted SSH command for that repository, the injected characters are executed, running arbitrary commands and exposing credentials in the context of the Image Updater process. No public exploit was identified at time of analysis; the only linked GitHub code is the vendor fix (PR #1905), not an exploit.